From: Eli Barzilay <e...@barzilay.org> > > > Most of the hit is due to doing the right thing wrt exceptions: > > > when there's an exception when a promise is forced, the exception > > > is stored as the "value" and will be re-raised when forced again. > > > > Yes. I believe this is right thing to do and I think (or want to > > think) that other languages, OCaml, Scala, F# or whatever, do the > > same. (I'll have to check myself...) > > I'll be interested in what you'd find out.
I'll get back to you about it. > > But the penalty is incurred only when an exception is raised during > > the initialization; am I correct? I.e, if the initialization is > > successful, no cost is incurred due to this. > > It's when the promise is forced (the important part). Hmm... I did not know installing exception handlers costs. But at any rate, I do not think I'll be willing to give up this semantics of memorizing exceptional behavior. > > Will you explain how/why it is fragile? It looks conceptually > > simple. > > Well, there were several problems that lead to memory leaks, which > means that it's hard to know about them, and it's hard to catch them > (I often resort to debugging with a process monitor). The code itself > has a number of subtle details that are important and easy to mess. It's well-thought-out rather than fragile, I would say :) Simplicity never means easy for me. > > You rewrite > > > > let rec x = y, y = M in E[x] > > > > into > > > > let rec x = M, y = x in E[x] > > > > The two graphs must be extensionally equivalent. > > (The racket code is not doing any rewrites, so I don't see how that's > related.) I thought this is roughly what the implementation does: In the first term x points to y and y points to M, in the second, x points to M and y points to x. (You kind of swap the pointers; so if y is not free in M nor E[x], it can be garbage-collected immediately.) Keiko _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
